Electrical resistance furnaces



March 1969 K. F. FAULKNER ETAL 3 ELECTRICAL RESISTANCE FURNACES Filed Nov. 13, 1967 //VV/V7ZPS KENNETH FRANCIS FAULKNER ET AL United States Patent 3,431,345 ELECTRICAL RESISTANCE FURNACES Kenneth Francis Faulkner and Alan Walter Plume, Ruislip, England, assignors to Heatlock Limited, Ruislip, Middlesex, England, a British company Filed Nov. 13, 1967, Ser. No. 682,227 Claims priority, application Great Britain, Nov. 14, 1966,

50,977/66 US. Cl. 13-22 Claims Int. (:1. H05!) 3/66 ABSTRACT OF THE DISCLOSURE This invention relates to electrical resistance furnaces, and is concerned, more particularly, with such furnaces of the type which includes a crucible for molten metal contained within a sealed enclosure so that the molten metal may be extracted, when required for use, from the crucible under the influence of pressure or vacuum.

It is an object of the present invention to provide an improved furnace of this type.

The present invention consists in an electrical resistance furnace of the type set forth, wherein a portion of a side wall defining the sealed enclosure is provided with a charging tube extending downwardly and inwardly to a point over the crucible, and means are provided for closing the charging tube allowing pressurizing of the enclosure.

In carrying the invention into effect according to one convenient mode by way of example, the accompanying drawing shows diagrammatically an electrical resistance furnace which includes a tubular shield 1 composed of a metal which may be a heat resisting steel, such as a non-corrosive nickel-chrome steel, capable of working in the range of 800 to 1250 C.

A crucible 2, preferably composed of silicon carbide, is supported within the shield 1 upon a bolster 3 of refractory material which rests upon a bed 4 of refractory material laid upon a bottom portion of an outer casing 5 of refractory material.

The shield 1 is provided at top and bottom with flanges 6 which engage refractory bricks 7 and 8 and further refractory bricks 9 are provided within the outer refractory casing 5.

The outer refractory casing 5 is enclosed by an outer steel casing 10 joined to a ring 11 secured t a top closure 12 so as to form a sealed enclosure containing the crucible, shield and refractory material.

An output tube 13 passing through the closure 12 is provided for extracting molten metal from the crucible 2 when pressure is introduced into the enclosure as hereinafter described.

The outside of the shield 1 is provided with a number of insulated supports 14 which carry heating elements 15 for heating the crucible through the shield 1.

The outer steel casing 10 is provided at the side with an emergency outlet in the form of zinc foil 16 clamped between an apertured plate 17 and flanges 18 adjacent an opening in the steel casing 10.

The foil 16 is sufliciently strong to withstand the pressure in the enclosure during casting (say 10-15 p.s.i.) but will melt should the crucible break or crack and discharge molten metal over the sloping surface of the bed 4 of refractory material onto the foil. This emerency outlet is of great advantage since in the event of a crucible failure the bottom of the enclosure would otherwise retain the molten metal which, on solidifying, would be diflicult to remove.

A thermocouple 19 is provided for monitoring the operating temperature in the region of the shield 1, with electrical connection to the heating elements being achieved by means of a terminal which passes from a protective cover 21 outside the steel casing 10, through the casing 10 a refractory material 5 and 9 to adjacent the heating elements 15. In order to achieve appropriate sealing of the casing 10 at this point, the terminal consists of an electrically conducting rod 20 upon which is mounted an insulator 22 having a metallic cap 23. The cap 23 is brazed to the rod 20 and the insulator 22 is bonded to a bush 24 mounted upon an insulated sleeve and screwed into the casing 10.

It is intended that the furnace described above should be charged with molten metal, for example from a sustaining furnace, and then the metal discharged as and when required in a pressure casting process, under pressure through the tube 13.

To permit charging and pressurization of the furnace, the outer steel casing 10 is provided in its side wall above the level of the top of the crucible with an apertured steel plate 25, through which is passed a cast iron charging tube 26 extending downwardly towards the crucible, and having an integral flange 27 bolted to the plate 25, with the tube 26 extending inwardly through the refractory material 5 so that its inner end.overlies the crucible 2.

To achieve sealing of the enclosure, the tube 26 is closed by means of a closure member 28 carried on a screw-threaded clamp 29 mounted on a bracket 30. The closure 28 is provided with a passageway 31 through which the interior of the enclosure may be pressurized.

To effect charging of the crucible, the closure member 28 is withdrawn by undoing clamp 29 and a funnel (not shown) is rested in the bracket 30 to facilitate pouring of the molten metal through the tube 26 into the crucible 2.

It is a feature of the furnace described above that should it be necessary to remove either the crucible 2 or the shield 1 for servicing purposes, then this may be done without removing the other component.

However, before this can be done it is necessary to withdraw the cast iron tube 26 and in order to prevent wear and tear upon the refractory material 5 during this step it is lined with a tube 32 composed of steel, such as one containing 25% nickel and 20% chromium.

This invention is not to be confined to any strict conformity to the showings in the drawings but changes or modifications may be made therein so long as such changes or modifications mark no material departure from the spirit and scope of the appended claims.

We claim:

1. An electrical resistance furnace, including a wall means and cover defining a sealed enclosure, a crucible for molten metal supported within said sealed enclosure, means extending into the crucible for extracting the molten metal, when required for use, from the crucible under the influence of pressure or vacuum introduced into the sealed enclosure, a charging tube having inner and outer ends, said tube being positioned in an aperture in said wall means and said tube extending downwardly and inwardly into the enclosure to a point where the inner end of the tube is above and in communication with the interior of the crucible, a closure member operably connected to said wall means for closing the outer end of the charging tube and said closure member having a passageway extending therethrough and by means of which said passageway interior of the enclosure may be pressurized.

2. The furnace according to claim 1, wherein said closure member operative connection comprises a clamp and a bracket for receiving and positioning a funnel to facilitate charging of the crucible when the closure member has been from the outer end of the tube.

3. The furnace according to claim 1, 'wherein the aperture in the wall means is lined with a tube.

4. The furnace according to claim 3 wherein the outer end of the charging tube is provided with a flange secured to the exterior of the enclosure around said aperture.

References Cited UNITED STATES PATENTS 11/1933 Granzer 219424 XR 5/1960 Tama 1333 XR BERNARD A. GILHEANY, Primary Examiner.

10 HIRAM B. GILSON, Assistant Examiner.

U.S. Cl. X.R. 139, 31 

